Editing Warhammer 40,000/7th Edition Tactics/Fortifications (section)

===For buildings only===
Small buildings can take one, medium buildings can take two and big buildings up to three of these upgrades. But you can only take one of each, so no double/triple void shields for you.
*'''Ammo store''' - Re-roll ones to hit when firing out from the building's fire points (but not the battlements). Useful, if you for some reason have a plasma gun team hiding in the bunker, instead of driving around in a transport. Unfortunaltely this also doesn't affect emplaced weapons, so you can't use it to ignore the Plasma Obliterators "gets hot".
*'''Booby Traps''' - The first unit to occupy the building would be blown up with 2D6 bolter hits (they also ignore cover saves). Only should be considered if you're planning on leaving the building unoccupied. Gets slightly better if you combine it with Magos Machine Spirit. Generally should be avoided.
*'''Escape Hatch''' - Extra access point for a building, you can place anywhere within 12", with the downside that you cannot assault out of it. One of the uses for it is to provide your shooty squad a nice escape route once the enemy comes close and personal, but generally ammo store is preferable for that purposes, as it allows you guys to kill things faster, rather than escape them when they cannot kill it fast enough.
** The escape hatch can be used offensively by some armies.  The hatch is placed in a forward position, allowing the embarked unit to go 12" forward, disembark 6", then shoot.  This option is slightly cheaper than a drop pod if you were taking the building anyway and can be used by armies without access to drop pods to great effect. 
*'''Magos Machine Spirit''' - BS3 for unmanned emplacement guns. Great. Good for giving Orks a source of BS3.
*'''Searchlights''' It's searchlights. Mostly useful for the shooty armies without their own sources of searchlights or night vision. By which I mean Necrons, especially with the Imotekh.
*'''Void Shields'''  This is often forgotten but all buildings can buy personal void shields, giving them and any models embarked within or on battlements a layer that must be popped before the target inside can be hit, making them immune to small arms fire. Any hits scored by shooting attacks that strike the building ''(or its occupants)'' will strike the shield <u>'''instead'''</u>  and have to be resolved against AV12. The rule does say that '''"after this"''' any further hits strike the original target, but because you are supposed to resolve all attacks from one weapon simultaneously, leftover hits after popping the shield cannot be reallocated to the original target, meaning that the building is completely protected from at least one single weapon for each void shield.
**Ranged D weapons don't even roll to penetrate, they just remove the shield. However, even if a D-weapon fires multiple times, they all strike the shield simultaneously, so excess hits are lost. 
**Smart opponent would pop the shield with S6-7 guns before unloading the heavy hitters on your building. But even then, the shield should take that autocannon or scatter laser fire from your other units for a turn or two.